During operation, a gas turbine engine compresses intake air, mixes the compressed air with fuel, and ignites the fuel-air mixture to produce combustive gasses, which are then expanded through a number of air turbines to drive rotation of the turbines and produce power. Significant quantities of energy are expended to compress the intake air before the hot, compressed air is supplied to the engine's combustion chamber for fuel injection and combustion. Leakage of the compressed air from the compressor section, especially from the downstream end of the high pressure compressor stage, results in a direct penalty against the engine's power-to-weight ratio and overall fuel efficiency. For this reason, air-to-air shaft seals are commonly positioned around the engine shafts to reduce the leakage of pressurized airflow from the high pressure compressor section and other such high pressure zones of the engine. Labyrinth seals have traditionally been utilized for this purpose, but are prone to degradation over time due to intermittent contact between the static components and the spinning disks or knives of the labyrinth seal. Finger seals can alternatively be employed in a gas turbine engine as an air-to-air shaft seal; and, in general, may provide higher pressure load capacities than do comparable labyrinth seals. Finger seals are, however, also subject to wear due to their contacting design and may require a relatively lengthy break-in process to ensure proper operation. Additionally, constant rubbing may occur between the fingers of the finger seal and the rapidly spinning shaft, which can potentially damage the finger seal or the shaft due to the generation of significant quantities of heat.
Finger-foil seals (also referred to as “lift-off finger seals”) have recently been introduced as an advancement over finger seals. A finger-foil seal may include a plurality of spiral-shaped resilient fingers, which collectively form an annular seal around the shaft in much the same way as do the fingers of a conventional finger seal. However, in contrast to a finger seal, the finger-foil seal further includes a radially-expandable aerodynamic foil, which extends around the inner circumference of the fingers and the outer circumference of the shaft. In addition to forming a high integrity, air-to-air seal around the shaft, the resilient fingers serve as a backing spring, which exerts a bias force on aerodynamic foil urging the foil radially inward toward the shaft. During high speed rotation of the shaft, the foil expands radially and lifts-off from the shaft in response to aerodynamic forces generated by rotation of the shaft. The resilient fingers deflect to allow foil lift-off, and a small annular gap is created between the spinning shaft and the aerodynamic foil. Physical contact between the foil and the rapidly spinning shaft is thus minimized reducing seal wear, reducing the generation of frictional heat, and eliminating the need for a lengthy seal break-in process. Further description of finger-foil seals can be found in co-pending U.S. patent application Ser. No. 13/316,922; filed with the USPTO on Dec. 12, 2011; entitled “GAS TURBINE ENGINE INCLUDING LIFT-OFF FINGER SEALS, LIFT-OFF FINGER SEALS, AND METHOD FOR THE MANUFACTURE THEREOF”; and assigned to Honeywell International Inc., the assignee and Applicant of the instant Application.
While finger-foil seals provide the above-described advantages as compared to finger seals, labyrinth seals, and other conventionally-known shaft seals, further improvements in finger-foil seals are still desired. Embodiments of improved finger-foil seals having increased pressure load capabilities are provided herein, as are embodiments of gas turbine engines including improved finger-foil seals. Other desirable features and characteristics of embodiments of the present invention will become apparent from the subsequent Detailed Description and the appended Claims, taken in conjunction with the accompanying drawings and the foregoing Background.